Various apparatuses are know for treating the inner parts of pipes and pipelines. The major differences between these apparatuses lie in the tool used for applying an essentially highly viscous preservative or sealing compound, the tools being moved by a suitable thrust means through the pipe length to be treated. The highly viscous compound is generally applied by centrifugal action or by pressure action. However, both types of application of the coating material have disadvantages. Thus, it is possible to centrifuge only those compounds, the viscosity of which is not too high. Since, however, sealing compounds must have very high viscosity, centrifuging can only be used in practice for coating inner walls.
Therefore, highly viscous compounds must be applied by pressure action. If, for this purpose, a circular extrusion nozzle is used, the necessary pressure is relatively high so that the production and controlling of very high pressure (of several hundred bars) is a costly matter, particularly when supplying the preservatives or sealing compounds from the outside. In addition, pressure extrusion is a continuous method although, in a relatively large number of applications, only particular areas of the inner wall have to be treated. This leads to a correspondingly and unnecessarily large consumption of preservatives or sealing compounds.